Add some metrics for printing with extension

Add some metrics for printing with extension

For now just recording user action for printing with extension and
page count for issued print requests.

Also, add missing histogram for page count when printing with privet.

BUG=None

Committed: https://crrev.com/0d79959841f0e42c720ea86f15e73c5bc0824734
Cr-Commit-Position: refs/heads/master@{#317460}

[tbarzic, 2015-02-20 18:09:31]

tbarzic@chromium.org changed reviewers:
+ isherman@chromium.org, vitalybuka@chromium.org

[Vitaly Buka (NO REVIEWS), 2015-02-20 18:13:10]

lgtm

[Ilya Sherman, 2015-02-21 00:26:39]

LGTM, thanks.

https://codereview.chromium.org/938193003/diff/1/chrome/browser/ui/webui/prin...
File chrome/browser/ui/webui/print_preview/print_preview_handler.cc (right):

https://codereview.chromium.org/938193003/diff/1/chrome/browser/ui/webui/prin...
chrome/browser/ui/webui/print_preview/print_preview_handler.cc:889: page_count);
I bet that UMA_HISTOGRAM_COUNTS_100 or _10000 would be better for this
histogram, but I understand if you want to keep it inline with the existing
histograms.  (Note that if you want to change the existing histograms to use a
different macro, you should rename those histograms as well, and mark the old
names as <obsolete> in histograms.xml.)

[Ilya Sherman, 2015-02-21 00:26:42]

The CQ bit was checked by isherman@chromium.org

[commit-bot: I haz the power, 2015-02-21 00:27:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/938193003/1

[commit-bot: I haz the power, 2015-02-21 00:50:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-21 00:51:09]

Patchset 1 (id:??) landed as
https://crrev.com/0d79959841f0e42c720ea86f15e73c5bc0824734
Cr-Commit-Position: refs/heads/master@{#317460}